Low-substrate-specific amino acid racemase, which is classified as EC 5.1.1.10 and whose substrate specificity is very low, is an enzyme useful for the industrial production of racemates of various amino acids. The microorganisms so far reported to produce this enzyme are strains belonging to the genera Pseudomonas [Methods in Enzymology, 17B, 629-636 (1971); Journal of Bacteriology, 175, 4213-4217 (1993)] and Aeromonas [Agricultural Biological Chemistry, 51, 173-180 (1987)]. However, their activity is often weak, and it is difficult to fully compensate this defect by improvement of culturing method or acquisition of a mutant strain.
With regard to the proteins having low-substrate-specific amino acid racemase activity, the protein produced by Pseudomonas putida IFO12996 has been purified and the amino acid sequence of its active site has been reported [Biochemistry, 23, 5195-5201 (1984)]. However, there has been no report on the DNA sequence encoding the enzyme or on a successful high-level expression of a protein having the enzyme activity using a microorganism such as Escherichia coli. 